# Rhombic drive crank pin Ø3 × 17

> What size crank pin does the rhombic drive gear take?

- Category: Stirling engines › Drives & mechanisms
- Kind: Hardware
- Basis: Ø3 pin at the gear's Ø3 crank-pin hole; 0.4 chamfer on one end; length = gear web + 1 mm + two links
- Page: https://xemstudio.com/objects/rhombic-crank-pin/ · JSON: https://xemstudio.com/api/geometry?object=rhombic-crank-pin · Plain text: https://xemstudio.com/objects/rhombic-crank-pin/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- The crank pin pressed into each rhombic gear 7 mm off its axis: Ø3 × 17 with a 0.4 mm chamfer on one end.
- It runs from the gear web's back face through the web (6, fit: press), a 1 mm gap and the lower and upper links (5 each, fit: run), ending flush with the upper link.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| crank pin | Ø3 × 17 | gear pin hole (press) and two link ends (run) | press | crank-pin-* |

## Sizes

| parameter | value |
|---|---|
| diameter | 3 |
| length | 17.0 |
| chamfer | 0.4 |

## Where the files are

- Wikipedia: [Rhombic drive](https://en.wikipedia.org/wiki/Rhombic_drive) — web — CC BY-SA 4.0 (text)
- Wikipedia: [Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine) — web — CC BY-SA 4.0 (text)
- Philips Research / Meijer: [The Philips Stirling engine (rhombic drive papers, 1958–1965)](https://en.wikipedia.org/wiki/Rhombic_drive#History) — web — reference (verify at link)
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/rhombic-crank-pin/index.json

- crank-pin-3x17: [STEP](https://xemstudio.com/files/hardware/rhombic-drive-kit/crank-pin-3x17.step) · [STL](https://xemstudio.com/files/hardware/rhombic-drive-kit/crank-pin-3x17.stl) — Ø3 × 17 crank pin: through the gear web, a 1 mm gap, the lower and the upper link

## How it fits

### Goes in or on
- [Rhombic drive crank gear, module 1.5, 44 T, 7 mm throw](https://xemstudio.com/objects/rhombic-crank-gear/): pressed in the Ø3 hole at 7 mm

### Connects to
- [Rhombic drive link, 30 mm centres](https://xemstudio.com/objects/rhombic-link/): two links turn on it

### Alternatives
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/): Ø3 pins

## Questions

**What pin goes in the rhombic crank gear?**

A Ø3 × 17 pin pressed into the Ø3 hole 7 mm off centre; two links turn on it.

**Why is the crank pin 17 mm long?**

Gear web 6 + 1 mm gap + two 5 mm links: it ends flush with the outer link, short of the yokes' plane.

## Fits with

- [Rhombic drive crank gear, module 1.5, 44 T, 7 mm throw](https://xemstudio.com/objects/rhombic-crank-gear/)
- [Rhombic drive link, 30 mm centres](https://xemstudio.com/objects/rhombic-link/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Crankshafts Ø3, Ø5 and Ø8 with full-length D-flat](https://xemstudio.com/objects/stirling-crankshafts/)